The present invention relates to an arrangement for transmitting electrical signals and/or energy between units mobile relative to each other, by means of a sliding contact arrangement.
For the transmission of electrical signals between units mobile relative to each other, sliding contacts are preferably employed. For linear movement, these contacts are also known by the term slideways, whereas for circular movement they are known as slip rings.
Such mechanical contact systems excel in simplicity and high sturdiness. For different applications, different contact pairings are available, which are selected based upon environmental conditions, contacting rate, and the electrical signals. When in the case of high contacting rates or high rotational speeds in the case of slip rings, a long service life is required and contact pairings are employed almost exclusively where at least one contact contains a combination of silver and graphite. In this combination, the silver is utilized to produce good electrical contact while the graphite serves lubricating purposes.
As has been demonstrated in tests, an excellent signal quality can be achieved with such a silver-graphite brush on an all-silver slideway. Transition resistance and even contact noise are particularly stable and low over long service periods. However, the high cost of this arrangement is a disadvantage. These disadvantages are felt particularly when large-size slip rings or slideway arrangements are used, because in these cases the slideways must be made of solid silver. When, because of excessive cost, a less expensive contact material such as brass or copper is utilized, these less expensive materials have a detrimental effect on the electrical transmission characteristics of the system. The transition resistance and contact noise may both be higher compared with the silver array, by up to two orders.
A known method of solving this problem is the application of solid brass slideways which are provided with a silver contact surface. Silver plating can here be made by a mechanical deposition of a silver coating or even by electrochemical treatment. The disadvantage of such an arrangement resides in the comparatively thin deposited silver layer. In case of high loads this layer can be worn off after a short time already and the brass slideway then remaining presents again very insufficient transmission characteristics.
The transmission characteristics of such sliding contacts are usually characterised by a number of electrical parameters. When high currents are transmitted the transition resistance is of particular importance. This parameter should be very low, preferably within the range of a few mxcexa9. Towards lower signal levels, which occur, for instance, in measuring and sensor signals, the contact noise is important as well. Such noise occurs during the movement of the contacts as a result of mechanical vibration, a change of the contact point and additionally on account of small electric arcs which may be formed between the two contact electrodes. Low contact noise is particularly important for a good signal quality.
The present invention is based on the problem of providing an arrangement for transmitting electrical signals and/or energy between units mobile relative to each other, by means of galvanic contacts and particularly a sliding contact arrangement, which will, on the one hand, offer a long service life and a high degree of reliability, even at high contacting rates, and, on the other hand, ensure an excellent quality in signal transmission.
One inventive solution to this problem is defined in Patent Claim 1. Improvements of the invention are the subject matters of the dependent Claims.
In accordance with the invention, at least one of the contacts presents a basic material having a high mechanical stability and into which, a second material that posses good electrical properties for the transmission of electrical signals and/or energy, is embedded. The second material is distributed in the basic material, so that at least one further contact that contacts the first contact, is in contact with the second material along the trajectory of its movement.
The invention hence combines the advantages of two different contact materials such as steel, brass or copper and silver. Here, the basic material, which is resistant to wear and inexpensive, serves as carrier of the arrangement whilst the second material, which presents good electrical properties, serves as contacting material. Due to this inventive configuration a particularly high transition quality can be achieved.
The contact consisting of a basic material, with a second material embedded therein, may be a slideway of a slip ring or contact brush, for instance.
The second material may be dispersed in the surface of the basic material, alternatively or additionally, the basic material may have at least one recess in which the second material is embedded. This recess may be a dovetailed groove, in particular, and with such a positive locking a particularly good connection is achieved between the two materials.
It is moreover expedient that the recess extends obliquely with respect to the sliding direction, in particular with an undulated course, at least in sections.
According to an alternative, the second material may be embedded in the form of several islets, i.e. contact areas externally separated from each other, or in the form of a trajectory in the basic material.
In any case it is advantageous, however, to vary the recess in terms of its extension or its shape orthogonally to the sliding direction in such a way that as a result of the contact with the sliding contact connection traces of the second material are rubbed into the basic material. On account of the sliding motion of the contacts minute particles of the second material having the good electrical properties are rubbed into the surface of the basic material, i.e. the solid contact trajectory, where they remain embedded in the surface as a properly conductive coating. As a result, the conductivity and particularly the contact noise as well as the transition resistance of the entire arrangement are substantially improved.
In yet another embodiment of the present invention, the second material is selected so that it is softer than the basic material. It can thus be easily transferred into the surface of the basic material.
It is moreover preferred to support at least one contact element element with a certain tolerance in a direction orthagonal on the main sliding direction. Owing to the small additional movements of the bursh transversely or obliquely to the main axis of movement, the second contact material can be better distributed over the contact trajectory consisting of the basic material. This may be achieved in a particularly simple manner by means of a suspension or support with high tolerances permitting a better bearing clearance. This can, of course, also be achieved by a selective control of the movement with guidance of the contacts so as to cause them to follow a predetermined trajectory.
In another expedient embodiment of the invention the trajectory of the second material is configured in a shape varying from the shape of the main trajectory of the arrangement. This may be a helical trajectory, for instance.
In the contact arrangement described above, which consists of a brush containing preferably an electrically conductive material and a lubricating material, where a contact trajectory comprises an electrically conductive material. It is therefore irrelevant whether these components are exchanged, i.e. a brush having an electrically conductive material on a contact trajectory comprising a combination of an electrically conductive material and a lubricating material such as silver and graphite. In such a case, the inventive arrangement would apply for the brush, which now contains two different conductive materials.